1. Field of Invention
This invention relates to methods and apparatus for adaptively controlling the propulsion of a series hybrid electric vehicle.
2. Description of Related Art
The desire for cleaner air has caused various federal, state, and local governments to adopt or change regulations requiring lower vehicle emissions. Increasing urban traffic congestion has prompted a need for increases in public mass transit services. All mass transit systems utilizes buses, at least in part, to transport people into, out of, and within traffic congested urban areas. Conventional buses use diesel powered internal combustion engines. Diesel engines produce emissions, including carbon monoxide, that contribute to air pollution. It is possible to refine cleaner diesel fuel. However, cleaner diesel fuel is more costly to refine and causes a corresponding increase in the cost of bus service.
Alternative fuels have been used to reduce emissions and conserve oil resources. Compressed natural gas has been used as an alternative fuel. Compressed natural gas does not produce as much power in conventional internal combustion engines as gasoline and diesel and has not been widely developed or accepted as an alternative to gasoline and diesel.
Additives have also been developed for mixing with gasoline to reduce emissions. Ethanol and MTBE have been added to gasoline to oxygenate the combustion of gasoline and reduce emissions of carbon monoxide. These additives, however, are believed to cause decreased gas mileage and, in the case of MTBE, to be a potential public health threat.
Electric vehicles have been developed that produce zero emissions. Electric vehicles are propelled by an electric motor that is powered by a battery array on board the vehicle. The range of electric vehicles is limited as the size of the battery array which can be installed on the vehicle is limited. Recharging of the batteries can only be done by connecting the battery array to a power source. Electric vehicles are not truly zero emitters when the electricity to charge the battery array is produced by a power plant that burns, for example, coal.
Hybrid electric vehicles have also been developed to reduce emissions. Hybrid electric vehicles include an internal combustion engine and at least one electric motor powered by a battery array. In a parallel type hybrid electric vehicle, both the internal combustion engine and the electric motor are coupled to the drive train via mechanical means. The electric motor may be used to propel the vehicle at low speeds and to assist the internal combustion engine at higher speeds. The electric motor may also be driven, in part, by the internal combustion engine and be operated as a generator to recharge the battery array.
In a series type hybrid electric vehicle, the internal combustion engine is used only to run a generator that charges the battery array. There is no mechanical connection of the internal combustion engine to the vehicle drive train. The electric traction drive motor is powered by the battery array and is mechanically connected to the vehicle drive train.
Conventional internal combustion engine vehicles control propulsion by increasing and decreasing the flow of fuel to the cylinders of the engine in response to the position of an accelerator pedal. Electric and hybrid electric vehicles also control propulsion by increasing or decreasing the rotation of the electric motor or motors in response to the position of an accelerator pedal. Electric and series type hybrid electric vehicles may be unable to accelerate properly if the power available from the battery or batteries and/or genset is insufficient.
Conventional internal combustion engine vehicles may also include systems to monitor the slip of a wheel or wheels to thereby control the engine and/or the brakes of the vehicle to reduce the slip of the wheel or wheels. In hybrid electric vehicles, however, it is necessary to control the speed and torque of the electric motor or motors to control the slip of wheels.
The invention provides methods and apparatus for adaptively controlling the propulsion of series type hybrid electric vehicles.
An exemplary embodiment of a series type hybrid electric vehicle according to the invention, including an internal combustion engine connected to a generator, a battery array receiving current at least from the generator, and at least one electric motor receiving current from the battery array, is adaptively controlled so that a command signal to the at least one electric motor follows and is proportional to a signal having a value indicative of a user demand. The vehicle propulsion is also adaptively controlled based on a state of charge and temperature of a battery array of the vehicle, an emission mode of the vehicle, a regenerative braking mode of the vehicle, and a nominal operating state of the at least one electric motor.
According to an exemplary embodiment, a method according to the invention for adaptively controlling propulsion of a series type hybrid electric vehicle including an internal combustion engine connected to a generator, a battery array receiving electric current at least from the generator, and at least one electric motor receiving current from the battery array, includes generating a first signal having a value indicative of a user demand, generating a second signal having a value proportional to the first signal and indicative of a demand of the at least one electric motor, determining if the value of the first signal is larger than the value of the second signal, increasing the value of a command signal to the at least one electric motor, if the value of the first signal is not larger than the value of the second signal, and decreasing the value of the command signal, if the value of the first signal is larger than the value of the second signal.
According to another exemplary embodiment, a series type hybrid electric vehicle according to the invention includes an internal combustion engine connected to a generator, a battery array receiving current at least from the generator, at least one electric motor receiving current from the battery array, a sensor that generates a first signal having a value indicative of a user demand, a controller that generates a second signal having a value proportional to the first signal and indicative of a demand of the at least one electric motor, determines if the value of the first signal is larger than the value of the second signal, increases the value of a command signal to the at least one electric motor, if the value of the first signal is not larger than the value of the second signal, and decreases the value of the command signal, if the value of the first signal is larger than the value of the second signal.
Other features of the invention will become apparent as the following description proceeds and upon reference to the drawings.